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I am back from the ion microprobe lab at Stanford after a few days of data collection, so I’ll be trying to get back on posting schedule here at Eruptions.UPDATE 3/10/2009 12:45PM: Here is a little (and I mean a little) more information, mostly adding that the local residents have been given a “warning” about the activity.
However, I did notice this morning at Sakurajima in Japan erupted after rumbling over the weekend. There aren’t many details about the eruption beyond the fact that volcanic chunks were thrown a few kilometers from the vent, but the BBC does have some nice video of the eruption (after the required commercial). From the looks of it, the eruption is a fairly typical Strombolian-style eruption that is common at Sakurajima.{Hat tip to reader Doug for the link to the BBC Video}

Galeras, in Colombia, appears to have entered a new cycle of activity as it has erupted for the second time in a week. A large explosion occurred this morning that was accompanied by falling ash and rocks (ballistic bombs) from the event. It is unclear how far the volcanic products travelled from the vent, but Colombian officials did raise the alert level back to red and ordered new evacuations.

Jonathan Castro has reminded me that I need a refresher on the proper terminology for ash columns related to volcanic eruptions. It is very easy to start mincing words and using them inappropriately – and that is the sort of sloppy reporting and discussion I am trying to avoid.
So, to refresh my (and our) memory on ash clouds and how to classify them, we can go back to one of the indispensable textbooks on volcanology, Cas and Wright’s Volcanic Successions. The classification scheme they provide is summarized in the figure above. It shows the heights of various eruption columns and the relationship between types of eruptions and their “explosiveness”. Jonathan is likely correct in classifying this eruption in the vulcanian range (<20 km ash column), especially if it was driven by explosions in the dome. If anything, Chaiten’s activity today could be sub-plinian, but a true plinian eruption requires a taller ash column height and higher levels of explosivity.UPDATE 2/20/2009: Here is a link to an article that talks about the processes that go along with each eruptive style. Remember, the ash column nomenclature is not solely dependent on height, but also process and composition. {Thanks to Boris for reminding me to emphasize this.}

UPDATE 2/19/2009 9:45 AM:Well, it seems that my hunch was at least partially right. Reuters (and Paula Narvaez, special envoy to the Chilean president) is calling the eruption as result of “what appeared to be a partial collapse of its cone.” So, we might have seen the oversteepening of the dome growing in the Chaiten caldera that lead to a collapse, producing (likely) a pyroclastic flow and either an accompanying plinian eruption as the pressure was released or an ash column associated with the pyroclastic flow itself. Now, I might not take Reuters word for it, but it makes sense considering the suddenness of the event.10:00 AM:More details for Reuters, including the ominous “Our security team have observed an increase in the size of a column of ash and smoke, with a deformation to one side” from the Deputy Interior Minister. My guess is he is referring to deformation on the ash column, not the volcano.4:00 PM: From a Newsday article, just some more details on the ash dispersal: “On Thursday, increased seismic activity was reported and ash fell 100 miles (160 kilometers) away in Futaleufu.”
—Eruptions reader Brian Owens has pointed out that fellow volcano follower, the Volcanism Blog, is reporting that Chaiten is experience a major rejuvenation today.
Sure enough, the Associated Press also reporting that an explosion has occurred in the main dome of Chaiten that has been built since last May and that material is moving downslope from the explosion. There is no clear word what type of volcanigenic material this might be – pyroclastic flow, lahars, avalanche – but there is a major fear that it could block the river and cause flooding in the town of Chaiten. The few citizens left in the area are being evacuated. The Patagonia Times adds that the eruption started around 11 A.M. (local time) and ash has spread across much of the region.
From what I can gather, this seems like it might have been either a dome collapse that was quickly followed by an explosion (possibly caused by the release of pressure from the collapse) or some “burp” of gas-rich magma erupting. The reports of “a massive column of ash” are interesting as this could suggest a true new flux of magma, but it is hard to tell at this point how widespread is the ash and how tall the column might be. At this point, it is all conjecture, but it sounds like Chaiten might be making a comeback. The questions woulds be how big and for how long.
I’ll update as we find out more …

I found this little press release that doesn’t have a huge amount of information, but is interesting nevertheless. The Coordinating Committee for Prediction of Volcanic Eruptions of Japan (nice name) is putting seven volcanoes on “24/7” monitoring. That sounds like we might see a lot of eruptions in Japan soon … except that their rationale was that these volcanoes “are likely to affect public life by erupting or becoming active in the coming 100 years”. That is quite the window of eruptive opportunity! The question is what exactly “24/7” monitoring – does this mean that someone/something will watch seismicity for signs of activity, or will this be a dedicated position that coordinates seismic, gas and deformation monitoring? The article doesn’t say much beyond seismographs and (vaguely) GPS. Nor does it mention what the seven new volcanoes are beyond Mt. Shirane and Mt. Norikura. However, I do give Japan credit for having such foresight when it comes to potential volcanic hazards.
One volcano that is already being constantly monitored is Mt. Asama, which has been erupting for over week. However, folks are already wondering when officials will say that Asama is “back to normal”. You can get a good idea of the ash dispersal from Asama with this excellent satellite image (above) from just after the January 21, 2009 eruption.

UPDATE 2/15/2009 20:30 PM: Marta Calvache of INGEOMINAS says that seismicity has all but stopped at Galeras after the eruption Saturday night, however the area will be kept on alert for more potential activity. However, even with the eruption, apparently there are very few people in the evacuation centers – never a good sign if something really big were to happen at the restless Colombian volcano.
Last night, Galeras, near Pasto in Colombia, erupted, prompting an evacuation of nearly 7,000 people living near the volcano. The first CNN article linked above, for some reason, says that Galeras is not in a “heavily populated” area, however over 500,000 people live in or around Pasto, which is quite close to the volcano itself (see the CCTV video footage or the picture above for evidence). The current eruption has blanketed Pasto in “abundant ash” (according to the mayor of Pasto), where there have no been reported injuries or death, however, they did have to close down two water treatment plants. Beyond this, not too much is known about this eruption as it is cloudy and rainy near the volcano. That being said, with this much ash being deposited, there is likely a plinian component to the eruption, making it likely to have been a larger eruption than many of the recent events at Galeras, the last ending in January 2008 (VEI ~2). {Hat tip to Jesse for pointing this out to me last night.}

I get a fairly steady stream of emails from Eruptions readers, some of which are very worth a post, but sometimes it takes me a while to get around to posting. This is my second attempt to catch up on these mailbag emails. Remember, feel free to email me questions or comments whether you want.

For those of you interested in what happens in the realm of submarine volcanism, I can pass on some tidbits I’ve gotten about NW-Rota 1, a submarine volcano in the Mariana Islands (see bathymetry above). Dr. Ed Kohut (Petrogenex), a friend of mine from my days at Oregon State Univ., is currently on a JAMSTEC research cruise in the Mariana Islands, visiting the area about NW Rota-1. He reports:

“We just reached NW-Rota 1. It is still actively erupting. To put that in perspective, it has been observed erupting every time it has been visited since 2003. Today’s actvity is not as vigourous as in past visits, but there are billowing sulfur laden plumes and the summit has increased ~15 meters since the last ROV visit (in ’06?).”

Seems that this seamount continues to chug away under ~500 meters of seawater. It is most famous for the 2004 eruption that coated an ROV that visited the volcano with ash and molten sulfur during an eruption (all under water). Below is a short video from a 2006 research cruise of the vigorous behavior at the vent called “Brimstone Pit”, which produced the 2004 eruption. You can clearly see the ash, rock and gases being ejected from the vent, all under half a kilometer of seawater!

Bored with waiting for Redoubt to erupt? Well, Nevado del Huila in Colombia looks like it is also on the eruption watch list. A fly-over of Huila performed by Colombian officials (unclear from the article if it was done by National Emergency Management or INGEOMINAS) revealed a large lava dome growing in the crater, suggesting that an eruption might follow considering all the lava being extruded. This eruption might come in the form of an explosion caused by the collapse of this lava done – the collapse itself could generate a pyroclastic flow and the release of pressure on the underlying magma from the collapse of the dome could prompt a plinian eruption as well (but this is all speculation on my part based on the short article). This type of activity would produce a larger eruption than we’ve seen so far during the rejuvenation of Huila that started in the fall of 2007. Evacuations are being recommended for all people living near the volcano.